Many structures are known for limited slip differentials, but they are complex and expensive devices. The following prior U.S. patents have been found in searches on the subject, but none provide a simple and inexpensive limited slip differential structure: U.S. Pat. Nos. 1,355,170; 1,483,606; 1,505,570; 1,515,916; 1,934,721; 2,859,641; 2,923,174; 3,548,683; 3,581,597; 3,686,976; 3,700,082; 3,732,750; 4,104,931; 4,400,996; 4,498,355; 4,507,984; 4,524,640; 4,554,845; 4,598,609 and 4,640,143.